I think 120+ is a tad optimistic for 8 lbs of A-trim boost. Also considering your free breathing engine I would not be suprised to see 6 pounds at the gauge. I think you would trap somewhere around 117-118.
My guess anyway.
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1988 Mustang GT
11.8 @ 123 (7/14/01)
11.5 @ 120 (9/14/01)
1992 BadAzz Wrangler
1993 Explorer
See my car at:
www.mustangworks.com/cgi-bin/moi-display.cgi?179